1. Field of the Invention
The present invention relates to a method and apparatus for pre-cooling humid gas to be supplied to an electric power plant as air for combustion or gasification of coal, with which heat transfer between the humid gas and cooling liquid in the heat exchanger tubes of the apparatus is increased resulting in improved heat exchange performance due to increased heat transfer efficiency.
2. Description of the Related Art
In gas turbine power plants, air compressed by a compressor is mixed with fuel and burnt in a combustor, and the high temperature combustion gas is introduced to a turbine to rotate it. Therefore, the air to be supplied to the compressor and mixed with the fuel is desirable to be large in specific weight in order to increase turbine output. The lower the temperature of air is, the larger the specific weight of air is. Therefore, air to be used in a gas turbine is desirable to be lower in temperature.
In production equipment of air for coal gasification to supply air to a coal gasification furnace in a compound power plant with coal gasification equipment, air for coal gasification is obtained by extracting a part of compressed air in compression process in the compressor of the turbine. In this case, also the extracted compressed air is cooled by a cooler to increase specific weigh thereof, thereby decreasing power required to supply the air. For example, cooling water of 30° C. is supplied as a cooling liquid to the cooler and compressed air of few hundred degrees (about 200° C. for example) is cooled to 50˜60° C. by the cooler. The cooling water rises in temperature to about 40° C. at the outlet of the cooler.
In patent literature (Japanese Laid-Open Patent Application No. 11-36887) is disclosed a suction air cooler having a number of heat exchanger tubes to cool the suction air. Construction of this air cooler will be explained referring to FIG. 11. In FIG. 11, suction air 010 is introduced from a suction air inlet 01 of a suction air cooler 02. A damper room 03, a suction air filter room 04, and a suction air duct 05 are connected to the cooler 02 so that cooled air is introduced to a compressor 07 of a turbine 06.
The suction air cooler 02 has banks of heat exchanger tubes 09 consisting of a number of heat exchanger tubes 08 arrange therein. Heat exchange is performed between a cooling liquid flowing in the heat exchanger tubes 08 and the suction air 010 flowing in the cooler while contacting the outer surfaces of the heat exchanger tubes 08 to cool the suction air. A drain pipe 011 is provided at the bottom of the suction air cooler 02 to drain water droplets generated by condensation of moisture in the suction air 010 and fallen down onto the bottom of the cooler 02. A plurality of dampers 012 are provided in the damper room 03 and the air stream is changed in accordance with whether the turbine is in an operation or halt.
A suction air filter 013 is provided in the suction air filter room 04 to remove dust contained in the suction air and cleaned air 010a is supplied to the compressor 07 of the turbine 06. The cooling liquid to be flowed in the heat exchanger tubes 08 is cooled by a refrigerating machine not shown in the drawing.
A plurality of trays 021 (two trays in FIG. 11) are provided to partition the banks of heat exchanger tubes 09 into several groups (three groups in FIG. 11) of heat exchanger tubes 08, and the trays 021 are inclined downward toward downstream of the suction air.
With this configuration, the suction air 010 flows through the space between the heat exchanger tubes 08 arranged in the suction air cooler 02 and is cooled by cooling liquid flowing in the tubes 08. Moisture in the suction air condenses and forms water droplets 019 on the outer surfaces of the tubes 08. The droplets gradually grow and fall down by their own gravity on to the trays 021. The water droplets 08 fallen down on the trays 021 flow down on the surfaces of the inclined tray 021 and then fall down from the downstream side end of each of the trays 021.
With this cooler, the water droplets condensed on the outer surfaces of the heat exchanger tubes 08 of each of the groups are gathered on the inclined trays 021 located below the tubes 08 of each group to fall down from the ends thereof and to form a kind of water droplet curtain 019a and are scattered so that they are contacted with the suction air flowing across the kind of water droplet curtain 019a in order to increase efficiency of trapping dust contained in the suction air. In this way, the water droplets 08 is allowed to perform subsidiary dust control effect for the suction air filter 013, thereby attaining long operation life and compactness of the suction air filter 013.
In patent literature 2 (Japanese Laid-Open Patent Application No. 2000161081) is disclosed an air suction device for a compressor of a gas turbine generator. The suction device is composed of a cylindrical air suction duct connecting to the inlet of the compressor. In the suction duct is provided a water spraying section, an air cooler, and an eliminator sequentially along suction air flow in the duct. A drain recovery and recycle section is provided outside the suction duct. The suction air is deprived of impure substance such as salt and sulfur content contained therein by spraying water in the water spraying section provided upstream of the air cooler and then cooled by the air cooler. Water droplets condensed on the outer surface of the heat exchanger tubes of the air cooler fall down and gathered to be reused as a part of water to be sprayed in the water spraying section. In this way, the suction air is cleaned in the water spraying section and then cooled by the air cooler only when temperature of the suction air is high in summer season.
The device disclosed in the patent literature 1 aims to increase trapping efficiency of dust contained in the suction air by utilizing water droplets condensed on the outer surfaces of the heat exchanger tubes and not intends to utilize the water droplets to increase heat transfer through the heat exchanger tubes.
With the device disclosed in the patent literature 2, water droplets condensed on the outer surfaces of the heat exchanger tubes are used as a part of water to be sprayed in the water spraying section to clean the suction air and not intends to utilize the water droplets to increase heat transfer through the heat exchanger tubes.